Add precompile signatures to Markdown to reduce latency. (#55715)
Fixes #55706 that is seemingly a 4472x regression, not just 16x (was my
first guess, based on CondaPkg, also fixes or greatly mitigates
https://github.com/JuliaPy/CondaPkg.jl/issues/145), and large part of 3x
regression for PythonCall.
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Co-authored-by: Kristoffer Carlsson <kcarlsson89@gmail.com>
